Famine will occur in parts of Somalia between October and December, the United Nations has warned, as a drought worsens and global food prices hover near record highs.

"Famine is at the door," UN humanitarian chief Martin Griffiths said at a news conference in Somalia's capital, Mogadishu.

The UN humanitarian chief explained he had concrete indications that famine would occur by autumn in parts of south central Somalia.

Somalia and its neighbours in the Horn of Africa, including Ethiopia and Kenya, are in the grip of the worst drought in more than 40 years, which has wiped out livestock and crops.

Humanitarian agencies have been ringing alarm bells over the deteriorating situation for months, with the UN's World Food Programme (WFP) saying last month that the number of people at risk of starvation across the region had increased to 22 million.

In Somalia alone, the number of people facing crisis hunger levels is 7.8 million, or around half the population, while around one million people have fled their homes in a desperate search for food and water, UN agencies say.

Mr Griffiths arrived in Mogadishu on Thursday for his first visit to Somalia.

He told reporters this morning that he had been "shocked to my core these past few days by the level of pain and suffering" he had witnessed.

"The clock is running - it will soon run out," he said.

A sandstorm in Dollow, Jubaland, southwest Somalia

The conflict-wracked country is considered one of the most vulnerable to climate change but is particularly ill-equipped to cope with the crisis.

A deadly insurgency by the radical Islamist Al-Shabaab group against the fragile federal government is limiting humanitarian access to many areas.

The UN's World Meteorological Organization has said the Horn was likely facing a fifth straight failed rainy season over the months of October to December.

In 2011, famine in parts of Somalia, one of the poorest countries on the planet, cost the lives of 260,000 people, more than half of them children under the age of six.